Generally, a front side member forming the front of the vehicle body is lengthily installed at both sides of the vehicle in the longitudinal direction of the vehicle. The bottom side of the front side member is coupled to a sub-frame to support the engine and transmission.
The sub-frame is coupled via a mounting bushing to the front side member. However, there is a drawback in conventional mounting bushings which provide a constant hardness once the shape and material of the rubber used in the mounting bushing are determined, thereby making it difficult to find an appropriate tuning valve according to various driving conditions of the vehicle.
For example, if the mounting bushing is decreased in hardness to decrease slight vibrations of the vehicle, rolling and bouncing increase. Rolling refers to a vehicle inclining to both lateral sides and bouncing refers to a vehicle moving up and down repeatedly. On the other hand, if the mounting bushing is increased in hardness for eliminating the rolling and bouncing, the amount of impact transmitted from the road surface is increased.
If the mounting bushing is decreased in hardness, the vehicle inclines to one direction, causing deterioration of the steering of the vehicle. If the hardness of the mounting bushing is increased to enable a good steering, the absorption of the road vibration and the steering are respectively deteriorated.
There is a drawback in conventional mounting bushings in that the mounting bushing is limited to a fixed shape and physical characteristics thereof, thereby rendering it difficult to enable both a comfortable vehicle ride and good steering.